Scaling is one of the most serious problems caused by water hardness, and its is a common one for industrial as well as drinking waters, at home or at restaurants, factories and so on. This particular by-product of heated hard water may put many water-using appliance out of service. It can clog hot water pipes and significantly reduce the heating efficiency of boilers or other water heaters due to deposit on interior surfaces. Moreover, water in most parts of the world is hard and needs to be treated to be of maximum usefulness.
Water quality is also part of efforts of consistent, reliable, vending/dispensing machine operations to deliver a consistent, high quality, safe product. Heating of hard water often leads to scaling, causing a host of problems such as inconsistency in water temperature, quantity of water delivered, eventual breakdowns of the heating units. The heating unit thus requires cleaning and sometimes repair.
Deposit from water formed during the water heating is generally classified either as scale or foulant. Scale is a hard, adherent mineral composition, which usually exists in crystalline form, while foulant is less adherent, tending to be amorphous or non-crystalline.
Scale deposition is a complex crystallization process which occurs when temperature, pH, concentration, flow velocity, pressure or other water conditions are changed. Firstly, an initial scale nucleus or layer is formed which then propagates. The rate of growth is determined by the interaction of several processes (e.g., supersaturating, nucleation, diffusion, chemical reaction and molecular arrangement of scale crystal lattices). Although the solubility limit must be exceeded for scale to form, the rate of scale formation can be controlled by the presence or absence of scale inhibitors and other factors.
Water usually contains a large number of potential scale-causing constituents, such as calcium and magnesium ions, soluble silica compounds, iron salts, and so on. Most calcium and magnesium salts because of their inverse solubility tend to form scale on heat transfer surfaces where the metal surface temperature is higher than the bulk water temperature. Scale usually contains, in order of prevalence, calcium salts (e.g., carbonate, phosphate, sulfate), magnesium hydroxide and salts, silica and silicates, irons oxides and hydroxides, zinc phosphate and hydroxide.
In the field of water treatment for commercial, industrial and domestic use, a number of methods and devices to reduce or eliminate scaling have been proposed, some or all of which have certain undesirable characteristics, drawbacks or disadvantages associated therewith
One of the common used techniques for water demineralization is reverse osmosis (RO). In most cases, it is probably the most efficient means of demineralization. In this method, water is pressurized through semi-permeable membrane to go over osmotic pressure (osmotic pressure is present when two liquids of different concentration are separated by a membrane). Another disadvantage of RO system is the cartridge design, which includes a “reject” stream that directs some or most of the water to waste before it can become so concentrated to cause clogging. Thus, ratio between purified and wasted waters can be 1 to 4 and even higher or reverse. Moreover, RO systems produce water relatively slowly; therefore the purified water is often collected in tanks for dispensing later. The capital and operational cost of above process is expensive, However, in certain installations (e.g. industrial and commercial water, large size vending machines), RO system may be of value.
Nanofiltration (NF) also uses semi-permeable membranes to filter water. Because of large overlapping in “pore” size of NF and RO membrane, NF is often considered as lower quality than RO. Further, NF usually removes 60–80% of polyvalent ions while RO—removes 98% and more, depends on membrane quality. A nanofilter, like RO membrane module, is designed with a continuous waste stream and has similar operational and economical disadvantages.
Another commonly used system is ion-exchange. Ions can be selectively removed from water by specific reactions using ion-exchange resins. Nowadays there is a range of ion-exchange resins with varying degrees of selectivity for cations and anions. Thus, during the water treatment, sodium, potassium and/or hydrogen cations are usually used to replace calcium, magnesium, iron and other polyvalent metal ions. However, regardless of the specific ion-exchange resins used, eventually the bed of the resin becomes exhausted and must be regenerated to become useful again or replaced. In addition, calcium replacement with hydrogen ions lowers pH, and both hydrogen and sodium could lead to undesirable taste and quality of water, and e.g. for coffee beverages.
Inorganic scale inhibitors are also commonly used to treat water against scaling. Among all inhibitors of scale formation allowed for drinking water, polyphosphates seem to work the best. One of the advantages of using polyphosphates is their lower effective concentration (usually 1–10 ppm) as compared to sequesters. In addition, polyphosphates are the cheapest anti-scaling agents. However, polyphosphates do not eliminate scaling; they delay deposit formation by slowing down rates of crystallization.
Reported effects of anti-scale magnetic treatment (AMT) of Water appear to vary widely, possibly reflecting variations in water quality. There has been a wide range of mechanisms proposed for how magnetic treatment works, however most of them are unproven. Furthermore, the apparent lack of AMT reproducibility has tended to undermine the credibility of the method.
Various metals, such as zinc, copper, or brass have been employed, in general, to treat water, but typically for other reasons, such as for reduction of levels of contaminants (chlorine, nitrates, hydrosulfide, etc.) in water and/or for bacteristatic/bactericidal functions. When employed in water, reduction of hardness has also been noted.
U.S. Pat. Nos. 5,433,856 and 5,314,623 disclose a fluid treatment method to remove calcium and magnesium. The method for treating water utilizes a bed of finely divided metal particulate matter, which comprises copper (and may/preferably also contain zinc) or can be in the form of brass alloy, e.g. KDF® material (KDF®-55 powder is the brand name for a granular alloy made of pure, lead-free brass, 50% Cu and 50% Zn). The method is said to lower mineral concentration, in particular, either calcium, magnesium or both, when water is passed through the redox alloy media. In this case, the calcium/magnesium compounds would be accumulated in the metal bed and eventually form a blockage. Moreover, the mechanism of lowering of calcium concentration in treated water is not described or understood.
To summarize known water treatment methods, scale inhibitors are effective in delaying time of deposit formation but do not eliminate scaling. The ion removal methods are most effective in scale prevention because of eliminating scale-causing constituents. However, the cost involved in adding of ions (mostly sodium or hydrogen) as in the case of ion exchange resins, as well as high pressure, an additional storage tank, operating costs in the case of RO, could be an issue.
Thus, there is a need for a method that is more efficient for removing the problem of scale in high cycle dispensing systems such as beverage and/or food dispensers. There is also a need for a low cost method to achieve these results and that is easy to implement. The present invention now satisfies these needs.